Petroleum production process



Mei-e12 Patented Feb. 16, 1954 PETROLEUM PRODUCTION PROCESS John W.Teter and Bernard S. Friedman, Chicago, Ill., assignors, by mesneassignments, to Sinclair Oil and Gas Company, Tulsa, Okla, a corporationof Maine No Drawing. Application December 17, 1948, Serial No. 65,974

6 Claims. (Cl. 166-21) This invention relates to the so-called secondaryrecovery of oil from partially depleted oilbearing formations, andparticularly is concerned with an improved method of washing out theformation by injection of a combined liquefied hydrocarbon and waterdrive.

One of the extraordinary things about the feared potential shortage ofoil is that several billions of barrels of oil remain in fully exploredand worked oil fields even after the best efforts of petroleumproduction engineers have been devoted to producing them for many years.For example, the Bureau of Mines has estimated that about five and halfbillion barrels of Pennsylvania grade crude oil remain in the knownAppalachian fields, but are non-recoverable by present recovery means.

Of course, one of the reasons for this anomalous situation is the factthat recovery of crude oil requires the expenditure of energy. Wherehigh reservoir pressures combined with ideal natural water drive andconservative production methods obtain, recoveries as high as 70 to 80per cent are possible. In general, however, it is a matter of commonknowledge that primary production, including pumping and vacuum methodswhere applied, rarely exceeds one-third of the total oil content, and inthe case of low pressure fields, such as the Nowata field of theBartlesville sand more often averages only about 15 to per cent. Theapplication of external energy to implement crude oil recovery isprimarily limited, of course, by the market price. However,re-pressuring with gas and water-flooding have been applied as socallcdsecondary recovery methods profitably in many fields to increaserecoveries by perhaps another 20 to per cent. We have now discovered animproved method of secondary recovery that obtains much higherpercentage recoveries, and, where geological and lithologicalcircumstances are favorable, permits nearly complete recovery of the oilcontained within the porous formation.

Cur new method is based upon the principle 3 of washing the oil-bearingformation with a material possessing a relatively high solubility forcrude oil so that the oil-connate water-sand \equilibrium is displacedby solution of the crude oil. A light liquefiable hydrocarbon or mixtureof liquefiable hydrocarbons is most useful for this purpose. Access ishad to the formation as by any of the systems of input and outlet wellsused in conventional secondary recovery. The light hydrocarbon isintroduced to the formation through the input well in the liquefiedstate, and advantageously, of course, back pressure is maintained uponsurrounding outlet wells. After sufficient liquefied hydrocarbon hasbeen introduced to saturate the formation immediately surrounding theinput well, water is pumped into the input well in order to drive theliquefied wash hydrocarbon towards the outlet well or wells. Oil and gasare recovered from the outlet wells by releasing the pressure.Advantageously, a vacuum is applied by pumping, and the hydrocarbon usedas wash liquid is recovered from the crude oil by fractionation.

We believe that our new method of secondary recovery produces greatlyincreased recoveries of crude oil because it positively displaces theoilconnate water-sand equilibrium. For example, we have found inlaboratory tests that a liquefied hydrocarbon, forced through a sampleof porous, partially depleted oil sand removes upwards of about per centof the total oil content in a single pass, while a light hydrocarbon gasfield drive recovers only about 15 to 25 per cent of the oil content bypressure purging. According to our method the layer of liquefiedhydrocarbon apparently washes out and dissolves the residual oil and thewater serves to convey the wash, oilbearing liquid layer through theformation to the outlet wells. The recovery of oil trapped or retainedby adsorptive forces, together with connate pane, butane, or a layer oflower boiling naphtha such as pentanes, hexanes, and the like may bellused. These hydrocarbons are water insoluble,..vv

but are readily liquefied, and may be readily re-.

covered with dissolved oil by releasing the pres-i sure or pumping avacuum on the formation} so that the wash liquid vaporizes from theinterstices and separates from the water.

Advantageo usly the,jormatign is scrubbed more than once with theliquefied hydrocarbon. TlTu'sTt'lie'formation is ordinarily subjected tothe combined liquefied hydrocarbon and water drive by pushing a layer ofliquid propane, for example, through the formation from an input well toan outlet well by means of a water drive. The propane-oil layer isrecovered at the outlet well and the propane separated from the oil andpumped back into the flooded formation at the input well. Thesecgdfipjeption of propane is then pushed through the formation byrepeated pu rnping of water into the input well. The drive may becontinued through additional cycles if desired.

Our new method thus may be applied to existing fields which have beensubjected to conventional secondary recovery by water drive. For

tilj dllll example, in the case of certain areas of the Nowata field ofthe Bartlesville sand, the original oil content was 17,750 barrels peracre, and the primary oil recovery 2,440 barrels, with vacuum andpressuring yielding another 3,981 barrel-s. Conventional water floodingyields approximately 3,764 barrels more, which leaves a residual oilcontent of 6,858 barrels per acre, amounting to 42 to 43 per cent of theoriginal oil content, as non-recoverable oil by known methods ofsecondary recovery. Again the method involves injection of a slug ofliquefied propane or butane, for example, at the input well followed bywater pumping to drive the hydrocarbon layer to the outlet wells.

Recovery of the hydrocarbons, that is wash liquid and oil, from the oilsand may be improved by the addition of surface-active agents; e. g.,alkalies, alkaline salts, acids, or acidic salts, to the water used inthe drive. It is advisable to select the particular agent on the basisof a trial conducted with cores taken from the formation in order toavoid emulsification difficulties. Obviously, surface-active agentshaving good wetting and penetrating action without appreciable oilemulsifying character are preferred.

Although our new method may utilize existing patterns of input andoutlet wells in fields where conventional secondary recovery methodshave been practiced, better results will be obtained by shortening thespacing between input and outlet wells. The advancing liquefiedhydrocarbon layer material becomes richer and richer in oil content asit progresses through the formation and, therefore, progressively losescapacity as a solvent for the residual oil. Hence, it is desirable tooperate so as to force the liquefied hydrocarbon; e. g. propane, througha length of oil sand limited, for example, to that containing residualoil which is soluble in propane in an amount approximating four or fivetimes the volume of the propane employed. The use of successive cycles,however, permits considerable flexibility in this respect.

One or more outlet Wells may be used for recovering oil and gas producedby our method, but as a practical matter several outlet wells as in thewell known five spot or nine spot patterns should be used. Advantage mayprofitably be taken of known methods of well packing and blocking tocontrol channeling which tends to reduce the recovery efficiency.

The principles underlying our invention will be illustrated in thefollowing example, which obviously, however, is not intended to be limiting with respect to field procedure or operating conditions. Theillustration describes a single pass, but recoveries are significantlyraised by repeating the cycle.

Exampla-A one-inch length of oil-sand core taken from the Nowata fieldin Oklahoma, was cemented inside a two-inch length of iron pipe. Bymeans of a suitable arrangement of pressure tubing and valves, w r wasdriven through the core, but the oil rec very was negligible.Approximately, three milliliters of liquefied propane was then driventhrough the same core under 210 p. s. i. g. inlet pressure (205 p. s. i.g. outlet pressure) by a fiow (A) of water. The layer of propane plusdissolved oil passed under pressure into a closed chamber where it wasisolated from the core. The pressure in this chamber was reduced and thepropane (B) allowed to gasify through a tube into a gas collectingbottle. The oil remaining was washed out of the chamber with pentaneinto a tared dish. After evaporation of the pentane on a steam bath, theoil residue in the dish was determined by weighing.

The quantity of propane (0) remaining in the core was determined byreleasing to atmospheric pressure and by pumping under vacuum. The

propane so released was collected and measured.

Finally, the amount of residual oil in the treated core was determinedby removing the core from the holder, powdering it in a mortar, andextracting with pentane in a Soxhlet extraction apparatus. Evaporationof the pentane yielded the residual oil. The results are tabulatedbelow.

Table Weight of core, grams 15.82 Volume of core, ml 7.46 Propanecharged, grams 1.5 Water charged (A), grams 10.0 Linear velocity ofcombined drive, feet/day- 5.0 Propane recovered (B), per cent 74.3Propane recovered (C) per cent 25.7

Oil recovered by propane, grams 0.095 Oil residue (by pentaneextraction) grams- 0.060 Weight-per cent oil recovered by propane" 61.3

We claim:

1. In the recovery of oil from partially depleted oil-bearingformations, the improvement which consists of introducing a liquefiednormally gaseous low molecular weight hydrocarbon to the formationthrough an input well while holding back pressure on an outlet well,forcing a layer of said liquefied hydrocarbon through the formation bymeans of water injection, and recovering gas and oil from the outletwell.

2. In the recovery of oil from partially depleted oil-bearingformations, the improvement which consists of introducing a liquefiednormally gaseous low molecular weight hydrocarbon to the formationthrough an input well while holding back pressure on an outlet well,forcing a layer of said liquefied hydrocarbon through the formation bymeans of water injection while recovering gas and oil from the outletwell, and additionally reducing the pressure within the formation so asto increase the recovery of gas and oil from the outlet well.

3. In the recovery of oil from partially depleted oil-bearingformations, the improvement which consists of repeatedly introducing aliquefied normally gaseous low molecular weight hydrocarbon to theformation through an input well, while holding back pressure on anoutlet well, and forcing a layer of said liquefied hydrocarbon throughthe formation by means of water injection while recovering gas and oilfrom the outlet well.

4. In the recovery of oil from partially depleted oil-bearingformations, the improvement which consists of repeatedly introducing aliquefied normally gaseous low molecular weight hydrocarbon to theformation through an input well, while holding back pressure on anoutlet well, and forcing a layer of said liquefied hydrocarbon throughthe formation by means of water injection while recovering gas and oilfrom the outlet well, and additionally reducing the pressure within theformation so as to increase the recovery of gas and oil from the outletwell.

5. In th recovery of oil from partially depleted oil-bearing formations,the improvement which consists of introducing a liquefied normallygaseous low molecular weight hydrocarbon to theformation through aninput well, while holding back pressure on an outlet well, forcing alayer of said liquefied hydrocarbon through the formation by means ofwater which contains a surfaceactive agent, and recovering gas and oilfrom the outlet well.

6. In the recovery of oil from partially depleted oil-bearingformations, the improvement which consists of introducing a liquefiednormally gaseous low molecular weight hydrocarbon to the formationthrough an input well while holding back pressure on an outlet well,forcing a layer of said liquefied hydrocarbon through the formation bymeans ofv water which contains a surfaceactive agent, while recoveringgas and oil from the outlet well, and additionally reducing pressure,

within the formation so as to increase the recovery of gas and oil fromthe outlet well.

JOHN W. TETER. BERNARD S. FRIEDMAN.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,787,973 Doherty Jan. 6, 1931 1,823,439 De Groote Sept. 15,1931 1,978,655 Straight Oct. 30, 1934 2,115,378 Wolf Apr. 26, 19382,341,500 Detling Feb. 8, 1944 2,412,765 Buddrus et a1 Dec. 17, 1946

1. IN THE RECOVERY OF OIL FROM PARTIALLY DEPLETED OIL-BEARINGFORMATIONS, THE IMPROVEMENT WHICH CONSISTS OF INTRODUCING A LIQUIFIEDNORMALLY GASEOUS LOW MOLECULAR WEIGHT HYDROCARBON TO THE FORMATIONTHROUGH AN INPUT WELL WHILE HOLDING BACK PRESSURE ON AN OUTLET WELL,FORCING A LAYER OF SAID LIQUEFIED HYDROCARBON THROUGH THE FORMATION BYMEANS OF WATER INJECTION, AND RECOVERING GAS AND OIL FROM THE OUTLETWELL.